Abstract

Cell-substrate interactions are of interest in modern biology. The system of surface bound hydrogels is commonly used as a cell culture surface in the field of cell biomechanics. However, the effect gel geometry (thickness, width and length) has on both the mechanics of the gel and the cells behaviour has usually been ignored.
It was discovered that a cell differentially spreads and preferentially accumulates at a certain position with respect to the local variation in thickness along a wedge gel (thickness varied from ~50 to 400 µm). This happened although this range of thickness is supposed to be sufficient to prevent the cells from sensing the underlying rigidity of the supporting glass. The mechanical anisotropy of the gel due to its being bound to the substrate was hypothesised to be the cause of the cell behaviour observed. It was later proven that lateral swelling varies exponentially with thickness. The consequences are the decrease in lateral compression and the lateral dilution of gel network density with increasing gel thickness. Both could cause variations of substrate mechanics. The amount of crosslinker, the geometry of the bound area and type of bathing medium all changed the degree of lateral swelling, and thus are contributing factors influencing the lateral mechanics of the swollen gel.
Surface bound square gels (50-2000 μm thick) were found to be stiffer with increasing thickness as measured with an atomic force microscope (AFM). This could be due to a change in osmotic pressure. These indentation based measurements of vertical mechanics might be of little relevance with respect to the cellular response though. This was supported with another set of cell experiments on such samples, where the cell did not respond in accordance with the stiffness as measured by AFM. It was therefore implied that the difference in cell behaviour observed on the substrates of different height might be a result of an interplay between the lateral mechanics and the rate of liquid flow though the gel.
The x-, y-aspect ratio was also found to influence cell alignment. Cells tended to align randomly on square (aspect ratio: 1:1), and perpendicular to the direction of the long axis of the gels in high aspect ratio (1:4 – 1:11) gels. This preference could be impaired by inhibition of the interaction between actin and myosin II using blebbistatin treatment. This suggests that actomyosin activity is necessary for such the behaviour.
The set of studies stressed the importance of x-, y- and z- macrogeometries of surface bound gels as these factors influence mechanical surface anisotropy. These results could have an implication not only in pure cell biology and cell biomechanics but also in regenerative medicine, physiology, wound healing, embryo development, and oncogenesis, wherever cells are in contact with soft biomaterials or orient themselves with respect to mechanical or other features

Item Type:

Thesis
(PhD)

Qualification Level:

Doctoral

Additional Information:

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